When you paste from your clipboard into a github issue, it will give you something like this:

Simply change to either of these formats:
For percentage size change
<img src="https://user-images.githubusercontent.com/16319829/81180309-2b51f000-8fee-11ea-8a78-ddfe8c3412a7.png" width=50% height=50%>
For fixed size (pixels)
<img src="https://user-images.githubusercontent.com/16319829/81180309-2b51f000-8fee-11ea-8a78-ddfe8c3412a7.png" width="150" height="280">

Thank you so much!